Automation Account with Hybrid Runbook Workers and Private Endpoint

Taranjeet Malik 171 Reputation points


We’re implementing a custom solution using the Azure Automation Account and Hybrid Runbook Worker nodes (on-premises) in a spoke Subscription / VNet as per the architecture below:

Private Endpoint n DNS Resolution - Neutralised Diagram

Basically, we have a hub VNet (where we got no control and do not want to deploy any service that belongs to our solution) where the ExpressRoute circuit is terminating from on-prem.

The Automation account needs to talk to on-prem services like Microsoft SQL DB and AD DS for which Hybrid Runbook Workers have been placed. The Automation Account is secured behind Private Endpoint and had Public Endpoint completely disabled.

To enable Hybrid Runbook Worker nodes to be able to resolve the Private Endpoints (FQDNs of the JRDS and Agentsvc services) of the Automation Account, following measures have been employed:

  1. Deployed DNS Private Resolver service with an Inbound Endpoint within a dedicated subnet (as it needs one) in the spoke VNet / Subnet (Subnet02). I’ve read some blogs that confirm this is a valid architecture and works – any additional configuration (DNS zone linking etc.) required on Hub VNet?
  2. Configured two-way VNet Peering between the Hub and Spoke VNets
  3. Configured a DNS Conditional Forwarded in the on-premises AD-integrated DNS server as follows:
  • DNS Domain Name:
    • Forwarding IP: Subnet02 IP that’s assigned to Inbound Endpoint of DNS Private Resolver service.
  1. Ensured that the on-premises subnet ranges for the Domain Controllers (with DNS) and Hybrid Runbook Workers are advertised to Azure over the ExpressRoute Private Peering connection.
  2. Azure Arc agent deployed on the VM (Azure Arc Private Link Scope is not used - is this required in this scenario?)
  3. Appropriate Firewall rules are in-place to allow the following:

Allow DNS (TCP and UDP 53) traffic from on-prem AD-integrated DNS to entire Subnet02 (where the DNS Private Resolver’s Inbound Endpoint is deployed). Do we need to allow DNS traffic for the whole Azure IP space, including the Hub VNet address space?

Allowed outbound 443 to the Global URL of the Automation Account, i.e., *

This is as per the article:

There’s no proxy on the way from on-prem to Azure along the ExpressRoute to intercept the outbound TCP 443.

The issue I’m seeing is that when I push the Extension-based (V2) Hybrid Runbook Worker agent on the nodes from the Azure portal, it fails with this error:

VERBOSE: [2023-05-17 05:04:56Z] Invoking HybridWorkerService Enable ...

WARNING: Error while reaching the Hybrid Worker server. Retrying it for : 1 time after waiting for 6 seconds

WARNING: Error while reaching the Hybrid Worker server. Retrying it for : 2 time after waiting for 12 seconds

WARNING: Error while reaching the Hybrid Worker server. Retrying it for : 3 time after waiting for 24 seconds

WARNING: Error while reaching the Hybrid Worker server. Retrying it for : 4 time after waiting for 48 seconds

WARNING: Error while reaching the Hybrid Worker server. Retrying it for : 5 time after waiting for 96 seconds

VERBOSE: [2023-05-17 05:09:04Z] Error encountered handling extension configuration...

VERBOSE: [2023-05-17 05:09:04Z] [ERROR] {"Message":"Authentication failed for private links"}

VERBOSE: [2023-05-17 05:09:04Z] {

    "Exception":  {

                      "Message":  "{\"Message\":\"**Authentication failed for private links\**"}",

                      "Data":  {


                      "InnerException":  null,

                      "TargetSite":  {

                                         "Name":  "ExtractErrorMessageAndThrow",





                                         "MemberType":  8,

                                         "MetadataToken":  100663378,

                                         "Module":  "HybridRegistration.ExtensionWorker.dll",

                                         "IsSecurityCritical":  true,

                                         "IsSecuritySafeCritical":  false,

                                         "IsSecurityTransparent":  false,


                                         "Attributes":  134,

                                         "CallingConvention":  33,

                                         "ReturnType":  "void",

                                         "ReturnTypeCustomAttributes":  "Void ",

                                         "ReturnParameter":  "Void ",

                                         "IsGenericMethod":  false,

                                         "IsGenericMethodDefinition":  false,

                                         "ContainsGenericParameters":  false,

                                         "MethodImplementationFlags":  0,

                                         "IsPublic":  true,

                                         "IsPrivate":  false,

                                         "IsFamily":  false,

                                         "IsAssembly":  false,

                                         "IsFamilyAndAssembly":  false,

                                         "IsFamilyOrAssembly":  false,

                                         "IsStatic":  false,

                                         "IsFinal":  false,

                                         "IsVirtual":  false,

                                         "IsHideBySig":  true,

                                         "IsAbstract":  false,

                                         "IsSpecialName":  false,

                                         "IsConstructor":  false,

                                         "CustomAttributes":  ""


                      "StackTrace":  "   at 


exception)\r\n   at HybridRegistration.ExtensionWorker.ExtensionWorkerConnectUtil.RegisterGroupInDatabase(String 

token)\r\n   at HybridRegistration.ExtensionWorker.ExtensionWorkerConnectUtil.Connect(Uri endpoint, Int32 timeout, 

When I do a nslookup on the FQDNs of the Private Endpoints (Automation Account) from the Hybrid Runbook Worker nodes (that are using the AD-integrated DNS servers as their DNS), I receive the correct response (Private IPs).


If I enable the Public Endpoint of the Automation Account, the agent installation succeeds.

Even after enabling the Private Endpoint for the Automation Account, the extension-based Hybrid Runbook Worker agent is trying to connect to Public Endpoints and failing - confirmed this through logs at the Firewall.

Checked the 0.settings file on the worker node (on-premises) inside the directory C:\Packages\Plugins\Microsoft.Azure.Automation.HybridWorker.HybridWorkerForWindows<version>\RuntimeSettings and this is what it shows:

User's image

Tracert from on-prem to Azure goes as far as the Microsoft Edge. No issue reported by the Network Watcher tests (Connection troubleshoot and IP flow verify) on Azure side. I deployed a test machine in the same VNet (Subnet01 – different subnet) where the Private DNS Resolver is located and the VM can resolve the Automation Account’s Private Endpoint FQDN to it’s private IP.



Any pointers / guidance will be highly appreciated.




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  1. Konstantinos Passadis 5,346 Reputation points

    Hello @Taranjeet Malik !

    I wold like to congratulate you for the detailed depiction of the issue ! Really great work !

    Your Architecture is exactly like this , or at least similar :

    Architecture diagram that shows name resolution traffic with Azure DNS Private Resolver when a spoke VM issues a DNS request.

    So i suggest to verify carefully and without any hastiness the following :

    1.     VM 1 queries a DNS record. The spoke virtual networks are configured to use the name resolution that Azure provides. As a result, Azure DNS is used to resolve the DNS query.

    2.     If the query attempts to resolve a private name, Azure Private DNS is contacted.

    3.     If the query doesn't match a private DNS zone that's linked to the virtual network, Azure DNS connects to Azure DNS Private Resolver. A virtual network link exists for the Spoke 1 virtual network. Azure DNS Private Resolver checks for a DNS forwarding rule set that's associated with the Spoke 1 virtual network.

    4.     If a match is found in the DNS forwarding rule set, the DNS query is forwarded via the outbound endpoint to the IP address that's specified in the rule set.

    5.     If Azure Private DNS (2) and Azure DNS Private Resolver (3) can't find a matching record, Azure DNS is used to resolve the query.

    Each DNS forwarding rule specifies one or more target DNS servers to use for conditional forwarding. Specified information includes the domain name, target IP address, and port.

    have you added the DNS Forwarding rule sets ?

    Spoke networks.

    • VMs are hosted in all spoke networks for testing and validating DNS resolution.
    • All Azure spoke virtual networks use the default Azure DNS server at the IP address All spoke networks are peered with the hub virtual network.
    • The spoke virtual networks are linked to private DNS zones, which makes it possible to resolve the names of private endpoint link services like

    It sure seems like a resolution thing !

    Let us know and post your feedback !

    I hope this helps!

    Kindly mark the answer as Accepted and Upvote in case it helped!


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